1. Field of the Invention
The present invention relates to a thin-film magnetic head in which magnetic saturation is controlled at the tip portion when a track thereof narrows.
2. Description of the Related Art
Recently, high densifying of magnetic recording density progresses. For example, in HDD system, a system which is feasible to realize the high recording density of 1 Gbpsi/inch.sup.2 becomes commercially practical, and it is nevertheless required to densify recording density. For achieving the high densifying of magnetic recording, such technical challenges as make a recording track of a thin-film magnetic head narrower in width, enlarge recording field with the thus narrowed track, and make magnetic inclination steeper in recording magnetic distribution in a line direction are remained for the persons in the art.
FIG. 18 depicts a structure of a thin-film magnetic head as a conventional and typical recording head. In FIG. 18, reference numeral 1 indicates a lower magnetic pole. An upper magnetic pole 3 is formed over the lower magnetic pole 1 with a recording magnetic gap 2 therebetween. The upper magnetic pole 3 has an air bearing surface (ABS) which is shaped corresponding to the track width. The upper magnetic pole 3 has a fan shape extending backward or to a coil (not shown) from the proximity of the air bearing surface. With the magnetic pole 3 having the shape shown in FIG. 18, the tip portion corresponding to the narrowed track width is hardly processed with high accuracy in the conventional manufacturing process of heads. Furthermore, magnetic saturation occurs at a narrow portion of the magnetic pole 3 (neck portion 4), so that it is difficult to generate large recording magnetic field.
For increasing recording magnetic strength, the same structure as that of the MIG (Metal In Gap) head which is used in a bulk head is conducted experiments on the thin-film magnetic head. A thin-film magnetic head provided with a magnetic material layer which has a high saturated magnetic flux density with an extra-thin thickness of about 0.2 .mu.m at a portion opposing to a magnetic gap is particularly known. When the recording track width of the thin-film magnetic head is narrowed, in a laminated film of two magnetic material layers with different saturated magnetic flux densities, the magnetic saturation occurs at the side of a lower saturated magnetic flux density layer. Accordingly, not only recording magnetic field strength decreases but also magnetic field inclination reduces, thus losing resolution, so that a disadvantage such as deterioration of NLTS (Non linear Transition Shift) happens.
A T-shaped thin-film magnetic head shown in FIG. 19 is also suggested to prevent magnetic saturation at a portion being narrowed near the tip of a magnetic pole. The thin-film magnetic head shown in FIG. 19 is provided, at the proximity of the air bearing surface of at least one magnetic pole (upper magnetic pole 5 in FIG. 19), with a magnetic pole chip 5a contacting with the recording magnetic gap 2 and an auxiliary magnetic pole 5b which is wider than the magnetic pole chip in a state to have T-shaped figure at the air bearing surface of the magnetic pole 5.
The T-shaped magnetic pole 5, as shown in FIG. 20, can be realized by means of opening a trench 7 with a predetermined track width in an insulation layer 6 formed on the recording magnetic gap 2 and forming by embedding magnetic material layers in the trench 7. In the T-shaped magnetic pole 5 using the trench 7, since the magnetic pole 5a can be changed in the shape and the position thereof in accordance with the shape of the trench, the magnetic pole chip 5a with narrowed track can be accurately obtained.
However, when the surface width of the magnetic pole chip 5a opposing to the gap is narrowed for ever-more narrowing of the track width in the T-shaped magnetic pole 5, the magnetic saturation occurs because of magnetic flux concentration at the laminated portion (the contacting portion) between the magnetic pole chip 5a and the auxiliary magnetic pole 5b. In this case, disadvantages of decreasing recording magnetic field strength and magnetic field inclination happen.
It is also investigated that the magnetic pole chip 5a in the T-shaped magnetic pole 5 is made with magnetic materials having a saturated magnetic flux density which is higher than that of the auxiliary magnetic pole 5b. However, the troublesome magnetic saturation at the laminated portion between the magnetic pole 5a and the auxiliary magnetic pole 5b is not completely prevented with the foregoing structure.
To be more specific, when the recording magnetic field is enlarged to increase the recording magnetic field strength, the magnetic saturation tends to break out at the laminated portion between the magnetic pole chip 5a and the auxiliary magnetic pole 5b. If the magnetic saturation occurs at the laminated portion, enough electric current can not be sent into the magnetic pole chip 5a made of the magnetic material having high saturated magnetic flux density, so that the magnetic field strength can not be improved in proportion to the increase of the recording current. Furthermore, the magnetic gradient in the line direction lowers because of magnetic field leaked out from portions where the magnetic saturation occurs, then raising a deterioration in NLTS.
As described above, the conventional thin-film magnetic head involves such disadvantage as tend to cause the magnetic saturation at any portion in the head when narrowing. Since the magnetic saturation in the magnetic head causes the recording magnetic field strength and the magnetic field gradient to lower and further NLTS to deteriorate, high densifying of the magnetic recording density is prevented.